For BMW E 90 323i 2009 model as far I know the head lights are D1S HID, just how can I check so to order the right one?
The first, and easiest, component to check is the headlight fuse. Depending on how your headlight circuit is set up, there may be one fuse or multiple fuses for the headlights. If you find a blown fuse, then replacing it may fix the problem. ... You should find battery voltage on both sides of the fuse.
See your Owners Manual for the location of this fuse. It is often located in the power center in the engine compartment, but may also be in the fuse panel under the dash. If the fuse has blown, replace it with a new fuse (same amp rating) and try again.
Problem: Both headlights do not work. The Cause: Most likely no voltage to the headlights because of a bad headlight relay, fuse, module, headlight switch, dimmer switch or wiring fault. It is often located in the power center in the engine compartment, but may also be in the fuse panel under the dash.
Many drivers think that a dim headlight is caused by a poor power connection. That's rarely the case. It's far more likely that vehicle is delivering enough power, but the ground connection is corroded, thereby reducing light output.